** Shares of derivatives exchange operator Cboe Global Markets CBOE.Z fall 1.9% to $216.13 premarket

** Morgan Stanley double downgrades CBOE to "underweight" from "overweight"; cuts PT to $215 from $256, a 2.4% downside to stock's last close

** Brokerage says sooner and better-than-expected tariff de-escalation with China reduces risk and volatility, which could limit upside to index option volumes on CBOE's exchanges

** Sees slower option volumes growth ahead with more downside risk to estimates, which could weigh on valuation with CBOE's shares trading at a premium to recent years

** 4 of 19 brokerages rate the stock "buy" or higher, 12 "hold" and 3 "sell"; median PT $228.50 - data compiled by LSEG

** As of last close, CBOE stock up 12.8% YTD

(Reporting by Arasu Kannagi Basil in Bengaluru)

((ArasuKannagi.Basil@thomsonreuters.com;))